The present invention relates to elastomer compositions including elastomers having functional groups, and compounds having additional functional groups. More particularly, the present invention pertains to elastomer compositions, in which functional groups of elastomers, and additional functional groups of compounds are capable of forming and cleaving cross-links reversibly with temperatures.
It is known, as described below, that an ionic bond, or a hydrogen bond is used for increasing a molecular weight of a monomer, or of a polymer, as well as modifying, or cross-linking the monomer or the polymer.
It was recently found that, when a polyallylamine and a long-chain alkyl acid are mixed, a salt is formed to generate a thermotropic liquid crystal. It was conceived that this phenomenon may have occurred, since the polyallylamine and the long-chain alkyl acid formed a salt within a range of temperature such that the salt would act as a methogen (Ujiie et al. Liquid crystal forum, 1997).
Onium salts with low molecular weights are widely used for preparation of, such as, an antistatic agent, an antimicrobial agent (JPA-9-111129), a gelling agent (JPB-2700377), a surface active agent (JPA-10-8041), a latent polymerization initiator (JPA-9-328507,JPB-2644301), and an energy ray-sensitive acid generator (JPA-9-202873). Moreover, polymeric compounds having onium salts, or their polymers are widely used for preparation of, such as, a pyridinium salt (JPA-9-324015), an ammonium salt (JPA-10-87741, JPB-2668260), a phosphonium salt-typed antimicrobial agent (JPA-10-81854), a monomer for soap-free polymerization (JPB-2668260), an antistatic agent (JPA-10-7822, JPA-9-328597), a film-forming perspiration-resistant polymer (JPA-10-500711), a water-soluble resin (JPB-2641955), a cross-linked polymeric ammonium salt (JPA-9-5007687), and a cleaner (JPA-9-235369).
However, a thermoplastic elastomer, in which a cross-link is formed by introducing an onium structure into a side chain of the elastomer, is not known. Moreover, an ionomer is known as a polymer having a cross-linked structure caused by a metallic ion.
It is a well-known fact that a hydrogen bond is formed between a carbonyl group and amine, and between pyridine and amine is seen in a biomolecule or the like. Immobilization of functional groups by hydrogen bonds is widely utilized in the ultramolecular-chemistry field, which is developing new functional molecules, such as an ion channel.
Moreover, it is also known that hydrogen bonds are utilized to modify thermoplastic resins. For example, JPA-63-69864 proposes a shape memory resin, which changes its shape by lowering the number of cross-links therein by heating it to over a grass transition point, but restores its original shape by cooling it to below the grass transition point. In JPA-63-69864, it is disclosed as a preferred embodiment that an epoxy compound and an amine curing agent are reacted to form a shape including a number of hydrogen bonds therein.
Furthermore, utilization of hydrogen bonds has been proposed to prevent heat resistance or rigidity from lowering, by adding a compound with a low molecular weight, or a thermoplastic resin with high flowability as a modifier. For example, a compound with a hydroxyl group, and a further compound with a functional group, which may form a hydrogen bond with the hydroxyl group of the former compound, are added into a thermoplastic resin such that flowability and heat resistance of the resin may be improved (JPA-5-339420). For an additional example, a thermoplastic resin, and a compound with a functional group, which may form a hydrogen bond with the following carboxyl group, are added to a styrene based resin having a carboxyl group such that rigidity and flowability of the styrene based resin may be improved (JPA-7-331002).
However, it is not known that a hydrogen bond is utilized for forming a cross-link between an elastomer and a compound.
Forming and cleaving of cross-links are known in polymer resins, but not known in elastomers. In other words, an elastomer having a conjugated diene structure including a heteroatom in its side chain is not known. It is also not known that, after a compound having more than two dienophiles, and an elastomer having a conjugated diene structure in its side chain are once bonded and cross-linked to each other by Diels-Alder reaction, the resultant cross-link is cleaved by heating.
Furthermore, an elastomer having a dienophile structure in its side chain is not known. It is also not known that, after the elastomer is once reacted with a compound having at least two conjugated dienes by Diels-Alder reaction to form a cross-link, which will then be cleaved by heating.
It is known that polyester having a furan moiety in its side chain is capable of cross-linking at 100xc2x0 C. in the presence of bismaleimide, and capable of cleaving a resultant cross-link at 140xc2x0 C. (U.S. Pat. No. 3,435,003). Moreover, the following two cases are also known (J. Polym. Sci., Polym. Chem. Ed. , 17 (1979) p. 2039, J. Polym. Sci., Polym. Chem. Ed., 17 (1979) p. 2055, U.S. Pat. No. 3,826,760 and U.S. Pat. No. 4,138,441):
After butyl rubber having cyclopentadiene is once cross-linked at room temperature, the butyl rubber will then be dissociated by heating in the presence of maleic anhydride; and
after ethylene-propylene rubber is once cross-linked at 150xc2x0 C., the ethylene-propylene rubber will then be dissociated at 170xc2x0 C.
Furthermore, it is known that a polymer having an oxazolidine or a furan shows a property of thermal cross-link formation and cleavage, which is capable of forming and cleaving cross-links reversibly with temperatures (Macromolecules, 1990, 23, p. 2636).
It is also known that, after resins having a furan skeleton react with bisdienophile to form a cross-link by Diels-Alder reaction, the cross-link will then be cleaved by heating (Macromolecules, 1998, 31, p. 2636).
Thermoplastic elastomers utilize physical cross-links, contrary to conventional vulcanized rubber having a stable three dimensional structure, in which a polymer and a vulcanizer form a covalent bond. The physical cross-links enable thermoplastic elastomers to be easily molded by the same fusion heating process as is applied to conventional thermoplastic resins. Therefore, it is not necessary that the thermoplastic elastomers employ a complicated vulcanizing and molding process including preforming.
As a typical example of such thermoplastic elastomers, a substance is known, which includes a resin component and a rubber component. At ordinary temperature, the resin component becomes a finely crystallized hard segment, which serves as a cross-link point of a three dimensional network structure. In this case, such hard segment prevents plastic deformation of the rubber component (soft segment) of the thermoplastic elastomers. However, as the temperature rises, the resin component is softened to melt. Then, the plastic deformation of the rubber component is allowed. Examples of such thermoplastic elastomers having a resin component and a rubber component are such as, for example, blockcopolymers such as a styrene-butadiene blockcopolymer, and an isoprene multiblockcopolymer, resin and rubber mixtures such as a mixture of polypropylene and ethylene-propylene dienecopolymer (EPDM). Moreover, a resin and rubber mixture, in which its rubber component (EPDM) is cross-linked by a peroxide, is also known.
Such thermoplastic elastomers, which have been known in the art, include a resin component as a hard segment such that rubber elasticity of the thermoplastic elastomers is undeniably lower than that of conventional vulcanized rubber. Accordingly, if a thermoplastic elastomer not including a resin component as a hard segment comes to be prepared, or, a vulcanized rubber comes to be provided with thermoplasticity properties (flowability), then, though a heat molding process without accompanying a complicated process of kneading, preforming, vulcanizing and the like, a rubber elastic body may simply be prepared. This will have a tremendous industrial advantage.
Though it is theoretically known that a thermoplastic elastomer may be obtained by utilizing a hydrogen bond for forming a cross-link, it is not known that such thermoplastic elastomer is in practical use. In other words, a hydrogen bond has a lower bonding energy than a chemical bond has such that the cross-link of the hydrogen bond is easily cleaved with heat and the like. Therefore, the resinous polymer described above is usually in a solid state at normal temperatures such that cross-linking is not required to solidify the polymer. However, the thermoplastic elastomer is transformed into a solid state by being cross-linked to exhibit rubber elasticity such that the elastomer may not be used in a cross-link mechanism unless it keeps a stable cross-linked state.
As far as rubber compositions for tires are concerned, a means to enhance processability of molding by decreasing viscosity through incorporating liquid polyisoprene rubber into diene based rubber is known (JPB-2727228).
On the other hand, JPB-2710263 discloses a method to enhance road-gripping properties of tires by incorporating liquid polyisoprene rubber having a hydroxyl group, and/or liquid polybutadiene rubber having a hydroxyl group into rubber. Moreover, JPB-2710264 discloses to enhance controllability of driving automotive vehicles safely by improving loss tangent (tanxcex4).
However, incorporating liquid polyisoprene into tires brought about problems. For example, tires have been lowered in tensile strength and abrasion resistance; the temperature of tires was raised by increased friction with roads since the loss tangent (tanxcex4) has come to be too large; and the like.
Accordingly, it is an objective of the present invention to provide an elastomer composition capable of forming and cleaving an ionic bond reversibly with temperatures, while having excellent heat resistance, low cold-flowability, and easy recycleability. Moreover, it is the objective to provide the elastomer composition to be added to adhesives so as to provide excellent heat resistance.
Another objective of the present invention is to provide an elastomer composition capable of forming and cleaving a hydrogen bond reversibly with temperatures, having excellent heat resistance, low cold flowability, and easy recycleability. Moreover, it is the objective to provide the elastomer composition to be added to adhesives so as to provide excellent heat resistance.
Still another objective of the present invention is to provide an elastomer composition capable of undergoing Diels-Alder reaction and reverse Diels-Alder reaction such that the elastomer composition is capable of forming and cleaving a cross-link reversibly with temperatures, having excellent heat resistance, low cold flowability, and easy recycleability. Moreover, it is the objective to provide the elastomer composition to be added to adhesives so as to provide excellent heat resistance.
Still another objective of the present invention is to provide a novel thermoplastic elastomer having a functional group capable of being a donor and an additional functional group capable of being an acceptor in a molecule when a hydrogen bond is formed. Moreover, it is the objective to provide the novel thermoplastic elastomer having a structure capable of forming a self cross-link, forming and cleaving a thermotropical cross-link reversibly, and further forming a stable hydrogen bond, which may substantially stand up to a temperature in actual use such that the thermoplastic elastomer has sufficient rubbery properties for actual use in place of rubber, and shows excellent flowability when heated.
The other objective of the present invention is to provide a rubber composition, which has excellent processability and tensile strength, excellent physical properties such as abrasion resistance, and small loss tangent (tan xcex4). The rubber composition is particularly preferable for the application of tires and the like of automotive vehicles.
To achieve the above objective, the present invention provides an elastomer composition, in which a functional group of an elastomer, and an additional functional group of a compound are capable of forming and cleaving a cross-link reversibly with temperatures. More particularly, the present invention pertains to an elastomer composition, in which the cross-link is an organic salt structure by an ionic bond. Moreover, the present invention pertains to an elastomer composition, in which the cross-link is a hydrogen bond. Furthermore, the present invention pertains to an elastomer composition, in which the cross-link is formed by Diels-Alder reaction. Still furthermore, the present invention pertains to an elastomer composition, in which the cross-link is intramolecular cross-link. And moreover, the present invention pertains to a rubber composition, which includes the elastomer composition capable of forming an ionic bond, and a solid rubber composition.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.